1. Field of the Invention
The present invention relates to an apparatus and method for detecting a printhead alignment of a printer. More particularly, the present invention relates to an apparatus and method for detecting a printhead alignment of a printer using an optical sensor having a single point focusing element.
2. Description of the Related Art
In the media printing environment it is important to assure that a printing onto a media is performed accurately. For example, in an inkjet printer environment, if the inkjet printhead is out of alignment, the ink will not print on a media in the proper position. To verify the alignment of a printing apparatus, typically an alignment detector is utilized to review predetermined marks made on a media to determine whether the printing apparatus that printed such marks is in alignment.
The alignment detector typically includes at least three components, a light source, an alignment sensor, and a housing to hold both the light source and the sensor, though the housing is not necessary.
FIGS. 1a and 1b illustrate examples of alignment sensors. FIG. 1a illustrates an alignment sensor that focuses light radiating off of surface/media 50 from area 60, using lens 110, onto a point position on phototransistor 100. When detecting a predetermined mark on a printed media the media is usually transported past the alignment detector, and a deviation in a detected signal is used as the indication of a predetermined mark. However, in the arrangement of FIG. 1a, because area 60 is quite large, the detection of the predetermined mark becomes difficult, as typically the predetermined mark is much smaller than such an area 60. In addition, the alignment sensor of FIG. 1a usually can only detect a relative intensity of a source reflected off surface/media 50. Such that when alignments patterns are printed in many blocks of parallel lines for each different alignment pattern of the printer, the alignment sensor can only measure the relative light intensity reflected off surface/media 50, and uses the pattern that appears darkest to align the printer. The darkest pattern represents the alignment that is one xe2x80x9calignmentxe2x80x9d factor form the best aligned pattern. Thus, this alignment sensor does not take into account the variations in the media and can be less accurate than point detection, as illustrated in FIG. 1b. FIG. 1b illustrates a different alignment sensor that focuses light radiating off surface/media 50, a point 70, using lenses 120 and 110, onto a point position of phototransister 100. In this configuration, the detection of the predetermined mark is more accurate, as point 70 is usually quite small. However, such an arrangement also has it""s drawbacks. To perform the point detection at point 70, the alignment sensor of FIG. 1b requires an additional lens 120. The alignment sensor of FIG. 1b may also include a filter to block out interfering light sources. Alternate alignment sensor systems may perform such point detection using even more additional lenses, rather than just lenses 110 and 120. When manufacturing multiple printing apparatuses, or any apparatus which have need of such an alignment sensor, the extra focusing elements excessively drive up costs of the alignment detector.
In an alignment detector configuration, the source may be a 640 nm red Light Emitting Diode (LED). Black and cyan inks absorb light at this wavelength and therefore may be detected when compared to the media background. The source LED wavelength can be changed if other ink colors require detection. For example, magenta ink will absorb light from 520-545 nm. A blue LED or white light source will allow all the ink colors to be detected. Typically, the color to mono inkjet cartridges require alignment as well as bidirectional printing from each printhead. Such alignments include mono bidirectional print for normal and draft modes, color bidirectional print for normal and draft modes, and mono to color horizontal and vertical alignment as well as skew alignment for mono printheads. FIGS. 2A and 2B illustrate examples of horizontal alignment. FIG. 2A illustrates the situation where a predetermined mark is out of alignment, while the predetermined mark is in alignment in FIG. 2B. The miss-alignment shown in FIG. 2A is evidence of the nozzles in a printhead being miss-aligned. As inkjet nozzle heights continue to increase, skew becomes an important measurement. Skew is the measure of how well the printhead is aligned vertically with the media. For example, a vertical line is printed in a full head height of the printhead and a second vertical line is printed in the same horizontal location but below the first line, as illustrated in FIG. 2C. The measure of skew is how well the top of the second line aligns with the bottom of the first line.
Previous implementations of printer alignment have been illustrated in Hubbard et al., U.S. Pat. No. 4,907,013, which illustrates a circuitry design for detecting a malfunction of an inkjet printhead, Lindenfelser et al., U.S. Pat. No. 5,534,895, which illustrates a method and apparatus for adjusting the quality of a printing, Matsuda, U.S. Pat. No. 6,084,607, which illustrates an inkjet printer detecting test patterns and detecting a deviation in the relative positioning of printheads, and in Beauchamp et al., U.S. Pat. No. 5,448,269, and Beauchamp et al., U.S. Pat. No. 5,975,674, both setting forth inkjet printhead alignment. However, none of these references sufficiently solve the aforementioned problems.
Thus, the present invention overcomes the problems associated with previous alignment detectors, including the inability of accurately detect predetermined printed marks on a media and performing such detection with a minimum number of elements.
An object of the present invention is to detect an alignment of a printer using an optical sensor having a single point focusing element
Another object of the present invention is to provide a printing apparatus, including a light source and an alignment sensor, wherein the alignment sensor includes a single focusing element to image a point on a media to a point on a detector. The printing apparatus also includes a control unit to determine whether the printing apparatus is aligned, based on a detection by the alignment sensor of a predetermined mark on the media.
Another object of the present invention is to provide a method of detecting a missalignment of an apparatus, including scanning a media for a predetermined mark, detecting the predetermined mark based upon an imaging of a point on the media, onto a point on a detector, by a single focusing element, and determining whether the apparatus is miss-aligned based on whether the detected predetermined mark is in predetermined position on the media.
A further object of the present invention is to provide an alignment detector, including a single focusing element, made of a translucent material, to focus an image of a point on a media to a point on a detector, wherein the area between the detector and single focusing element is filled with the translucent material.